findss.zsh

#!/usr/bin/env zsh

if [ -z $2 ]
then
    echo "Usage: $0 [options] source fragment"
    exit 1
fi
src=$1
frg=$2
testframes=400

matchframe=$(
    ffmpeg -hide_banner -loglevel error -i $src -i $frg -lavfi '
        [1:v] setpts=PTS*1000,fps=30,scale=100:100[frg-first-frame];
        [0:v]scale=100:100[ref];
        [ref][frg-first-frame]psnr=f=/dev/stdout' \
        -vframes $testframes -f null -y /dev/null |
    awk -F'[ :]' 'BEGIN{m=1000}; $4<m {n=$2; m=$4} END{print n}'
    )

ffprobe -hide_banner -loglevel error -show_frames -select_streams 0:v -of csv $src |
    awk -F, "NR==$matchframe {print \$5; exit}"